The blue wildebeest embark on their spectacular annual migration to follow seasonal rains and the growth of plentiful grasses. The timing can vary from year to year, depending on the weather. But generally by this point in the year, the giant herds are moving from the northern Serengeti in Tanzania across the border into Kenya’s Maasai Mara National Reserve, shown in this photo. The annual migration sees over 1 million of these grass-eating bovines crossing miles of African savanna, often following the plains zebra as they make similar trek. By December they’ll be back in Tanzania for the rainy season. Many of the nations where the wildebeest migrate recognize that keeping the migration safe and healthy draws in tourist money. Many parks and preserves are established along the migration route, ensuring the safety of the animals, and allowing humans to view this marvel in person.